The correct option is 1 and 2 only.
Explanation
In arid and semi-arid regions, running water acts as a primary agent of erosion, despite the scarcity of rainfall. The landscape evolution in deserts is characterized by specific erosional processes such as sheet floods and the retreat of slopes, which shape landforms like pediments and pediplains.
Statement 1 is Correct
Erosion in desert landscapes typically initiates along the steep margins of landmasses or mountain fronts. Through the process of backwasting (parallel retreat of slopes), the steep mountain front recedes, maintaining its steep angle while leaving behind a gently sloping, bedrock surface known as a pediment at its base.
Statement 2 is Correct
Rainfall in deserts is often torrential and of short duration. Due to sparse vegetation, the water does not infiltrate easily but flows as sheet floods (broad, unconfined flows) across the surface. These sheet floods are highly effective in removing weathered material and debris from the pediments and transporting it away from the mountain front.
Statement 3 is Incorrect
Stream channels in deserts are ephemeral, meaning they flow only for short periods following rainfall. Because of the high sediment load and rapid loss of water due to evaporation and infiltration, these channels tend to be broad, shallow, and braided. They are not narrow, deep, or permanent as seen in humid regions.
Key Takeaway:
Desert erosion is driven significantly by ephemeral running water in the form of sheet floods, which facilitate the parallel retreat of steep slopes, while desert stream channels are characteristically broad, shallow, and temporary.